Add more hsc3 related packages

This adds the following packages to the tree:

- [hsc3Dot](http://rd.slavepianos.org/?t=hsc3-dot)
- [hsc3Process](https://hackage.haskell.org/package/hsc3-process)
- [hsc3Db](http://rd.slavepianos.org/?t=hsc3-db)
- [hsc3Lang](http://rd.slavepianos.org/?t=hsc3-lang)
- [hsc3Server](http://hackage.haskell.org/package/hsc3-server)

It also fixes a package marked broken, hmatrix-special, by adding a dependency to [gsl](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/gsl/default.nix).
Please do *not* edit these files manually. (Note the comment at the top!) If there are missing dependencies, then these should be added via caba2nix's [PostProcess.hs](https://github.com/NixOS/cabal2nix/blob/master/src/Cabal2Nix/PostProcess.hs) module.